Information recording disks such as magnetic recording disks used, for example, in "hard disks," compact disks, etc. have a structure where a recording layer is formed on the surface of a substrate which is made of a metal or dielectric material. In one process for making a magnetic disk used in a hard disk, a substrate of aluminum (Al), or other suitable metal or dielectric material is first coated with a nickel-phosphorus (NiP) layer. Next, an undercoat metal film of suitable material (such as CoCrTa) is deposited on a surface of the substrate and then a recording layer made from a thin magnetic film of suitable material is deposited on the metal film layer. The recording disk is completed by the depositing of a protective layer over the recording layer.
The protective layer must be composed of a durable film which has lubricating properties in order to shield the recording layer from impact and harsh environments. For example, sputtered carbon films (carbon films which have been deposited by sputtering) have been commonly used as protective layers. Chemical vapor deposition (CVD) of carbon has also been used to provide the protective layer. For ease of description, a protective layer consisting of carbon shall be referred to herein as a carbon protective layer.
With the recording density of hard disks continuing to increase, it has become necessary to provide carbon protective layers having a reduced thickness as compared to those conventionally used in the past. Greater recording density means less space between the sectors on the hard disk. When the space between sectors is reduced, the distance between the recording head and the magnetic recording layer must also be reduced. Currently available hard disks have a recording density of 1.6 gigabytes per square inch. Because the carbon protective layer is deposited on the magnetic recording layer, the thickness of the carbon protective layer must be reduced in order to minimize the distance between the recording head and the magnetic recording layer. Current commercial embodiments use films of between about 100-150 A. This is expected to be reduced to 50-100 A.
FIG. 13 is a schematic plan view of a conventional plasma CVD film deposition chamber. The deposition chamber 6 is equipped with a pumping system 61, a process gas delivery system 62 for introducing a process gas into the film deposition chamber 6, plasma generating means 63 forming a plasma by providing energy to the process gas which has been introduced by the process gas delivery system, and a transfer system (not shown) used to transfer a substrate 9 inside the deposition chamber 6.
The process gas delivery system 62 is designed to introduce an organic compound gas such as methane (CH.sub.4) into the interior region of the deposition chamber 6. The plasma generating means 63 is designed to form a plasma by providing high frequency rf energy to the process gas, and is comprised of a high frequency power source 633 for supplying high frequency electrical power by way of a matching box 632 to a high frequency electrode 631. When plasma of a gas such as methane is formed, the gas in the plasma decomposes resulting in a thin film of carbon being deposited on the surface of the substrate 9. The deposited layer of carbon is then polished to a prescribed thickness.
Carbon films may be broadly divided into amorphous carbon films and crystallized carbon films. Crystallized carbon films are generally made of graphite, but some have a lattice structure similar to a diamond and are referred to as diamond-like carbon (DLC) films. In the manufacture of carbon films by plasma enhanced CVD using a hydrocarbon compound gas such as methane, when energy is provided by the collision of negative ions, a reduction in C--H bonds and C covalent bonds in the plasma occur which results in more C single bonds thereby resulting in a film having a diamond lattice structure.
A drawback associated with conventional film deposition apparatuses used to form carbon protective layers is that during the deposition process the carbon, used to provide the protective layer on the hard disk, is also deposited on the exposed surfaces inside the deposition chamber. As the carbon film buildup increases within the deposition chamber, the film separates as a result of internal stresses, gravity, etc., resulting in undesirable carbon particles being released inside the deposition chamber. These undesirable particles adhere to the surface of the substrates inside the chamber, forming protrusions on the surface of the protective layer, resulting in local irregularities in film thickness which can cause head crashes or signal errors.
FIG. 14 is an exploded, cross-sectional view of the surface of an information recording disk and a device used to detect defects on the surface of the disk. When the carbon protective layer is deposited with the particles adhering on the substrate surface, protrusions 902 are formed as shown. The particles and the protrusions resulting therefrom can have a diameter in the range of between about 0.1 to 0.5 microns.
To detect the presence of such protrusions, a glide height test is performed after the carbon protective layer is deposited on the magnetic recording layer. The glide height test is a test in which a tip 904 of a detector 903, as shown in the dashed outline in FIG. 14, is used to scan the carbon protective layer 901 while being held a predetermined distance above the surface of the protective layer. In present applications, the distance d is set at 1 micro-inch. When the tip 904 contacts a protrusion 902 a short circuit is generated within a detection circuit (not shown) which provides an indication that the hard disk contains a protrusions of sufficient size to make the hard disk defective.
In conventional film deposition apparatuses, a considerable amount of carbon particles may be produced by the separation of the carbon film deposited on the exposed surfaces in the processing chamber which, in turn, cause many carbon particles to contaminate the surfaces of substrates. It is difficult to remove all the protrusions and smooth the substrate in subsequent processing steps. Furthermore, when large protrusions are deposited by the accumulation of carbon particles, attempts to remove the protrusions can lead to problems such as scratches or pitting on the surface of the substrate. Such scratches or pitting might pass the glide height test, but often are considered defects in subsequent certifying tests (i.e. recording and playback tests). A drawback associated with conventional film deposition apparatuses has thus been the inability to reduce the incidence of product defects.